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How Crops May Be Changing Weather

Bryce Anderson
By  Bryce Anderson , Ag Meteorologist Emeritus
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Image by David L. Hansen

A little over a year ago, researchers at the Massachusetts Institute of Technology (MIT), in Cambridge, Massachusetts, used computer modeling to try to unravel a temperature mystery: the fact that, during a worldwide warming trend, the central U.S. has seen summer temperatures actually cool by as much as a full degree Celsius (more than 2 degrees Fahrenheit), and rainfall increased up to 35%, the largest such increase anywhere in the world. And, as it turns out, the size of the crop canopy is the reason.

We know how corn production has increased in the U.S. The Corn Belt now extends from the Texas Panhandle north to North Dakota and east to Ohio. Since 1950, corn production has gone from around 2 billion bushels to more than 15 billion bushels in 2017--a sevenfold increase.

The MIT research project used computer modeling to analyze five different 30-year climate simulations, using data from 1982 to 2011. The team first compared simulations with high levels of intense agriculture (dense planting) to simulations with no agricultural influence. Unlike the real-life climate changes, the control simulations showed no change in temperature or rainfall. But, more than 60% of the simulations with intense agriculture resulted in temperature and rainfall changes that matched the observed changes.


The researchers’ results were far different than forecast models which did not account for agricultural use. Model iterations that did not factor in agricultural activity failed to match the observed changes in U.S. Corn Belt weather patterns. The indication is that agriculture is the cause of the regional changes in climate during the past 30 to 40 years. In other words, thick rows of corn (and soybeans) likely counteracted rising temperatures regionally that might have otherwise resulted from higher levels of greenhouse gas emissions. It’s not just the U.S. where this feature is noted, either; eastern China, which has intense agriculture, has logged a similar cooler temperature trend.

The reason for this “thermostat”-type effect is in the photosynthesis process for crops. When a plant’s pores, called stomata, open to allow carbon dioxide to enter, they simultaneously allow water to escape. This increases the amount of water going into the atmosphere and returning as rainfall. That rainwater eventually moves back into the atmosphere and causes more rainfall downwind from the original agricultural area.

How long this crop-influenced milder temperature pattern will last is up for question. Some scientists question whether agricultural production could soon hit its limit in many parts of the globe. Nonetheless, the MIT study opens an interesting new aspect of understanding the interaction of agriculture--food production--and a changing climate.

Note: The MIT research findings were first published in “Geophysical Research Letters.”

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